On the Babylonian Sighting-Criterion for the Lunar Crescent and its Implications for Egyptian Lunar Data

Abstract

The aim of the present paper is to establish a lower boundary condition of a possible successful sighting of the lunar crescent based on Babylonian predictions and observations. This means that all Egyptian chronological options showing deviations in positive direction with visibilities below this boundary condition will be dismissed as impossible. Although a theoretical limit of 10° for the visibility criterion, i.e. a minimum lagtime between sunset and moonset of 40 minutes, is mentioned in text TU 11, the Babylonian Astronomical Normal Star Almanacs contain several predictions for first or last visibility with values smaller than 10° and the Astronomical Diaries a few such observations. Thus, a value of 10° for the lagtime is an inappropriate lower boundary condition which cannot be used as knock-out criterion for Egyptian chronological options based on lunar data.